Bone marrow stromal cells (BMSC) have a great potential in the treatment of myocardial disorders. Due to their malleable nature, BMSC possess multi-lineage potential and can overcome lineage restrictions to form non-hematopoietic tissues including myocardium. There is unflinching evidence that mononuclear cells emigrate from their bone marrow niches in response to tissue ischemia and become blood borne. These cells show tropism for the ischemic myocardium where they undergo milieu dependent transformation and develop into functioning cardiomyocytes. Our long term goal is to exploit BMSC as a therapeutic modality to regenerate the infarcted myocardium and revamp the injured heart function. The proposed study addresses some fundamental issues pertaining to both in vitro as well as in vivo fusion and transdifferentiation potential of ischemically mobilized BMSC to form cardiac myocytes. We postulate that ischemically stressed myocardium provides a strong trigger to initiate mobilization of specific sub- populations of BMSC into peripheral circulation. The blood-borne cells home onto the injured myocardium to adopt cardiac phenotvpes and improve cardiac function. Characterization of BMSC committed to cardiac lineage will help to understand the basic mechanisms underlying BMSC mobilization and differentiation both in vitro and in vivo conditions. Three main hypotheses fundamental to the proposed project include: 1) ischemic stress mobilizes specific population of BMSC cells into peripheral circulation: 2) Mobilized BMSC undergo milieu dependent differentiation into cardiomvocvtes and endothelial cells to promote cardiomyogenesis and angiogenesis: 3) Mobilized BMSC protect myocvtes against ischemia by secreting specific factors. The experimental design involves the use of BMSC from transgenic mice expressing enhanced green fluorescent protein. Co-culture cell model will be used to study the biology of BMSC in vitro. Their potential to differentiate into cardiac phenotypes in a cardiac microenvironment using murine heart model of myocardial infarction will be examined. The effect of ischemia on BMSC mobilization in peripheral circulation and finally their engraftment in the ischemic area will be studied. The mechanism by which BMSC survive in the ischemic environment and protect myocytes will be investigated by examining the molecular mediators, such as growth factors, cytokines, paracrine factors, secreted by the BMSC. A broad multidisciplinary approach that will encompass diverse techniques including histochemistry, immunocytochemistry, pathology, flow cytometric analysis, confocal microscopy and molecular biology will be used to investigate the specific aims. A complete understanding of the ongoing molecular processes in stem cell mediated regeneration is central to the success of cell derived-therapy.